1. Field of the Invention
This invention relates to the field of sensors for detecting biological agents such as toxins, viruses, spores, bacteria and other pathogens, and to detect chemical agents as well. More particularly, it pertains to the use of a morphological change in the material of the sensor when a target pathogen or vapor interacts with the sensor. The sensor is inexpensive, sensitive, selective, robust, and covertly deployable.
2. Description of the Related Art
The need for detection of chemical and/or biological agents in a variety of applications is acute. A number of methods have been developed which allow such detection. However, none of the methods described in prior art is quite acceptable, as discussed below.
The present invention, as subsequently discussed, applies the concept of using indicator molecules for such detection as these indicator molecules are first ensconced on electroconductive polymer carriers.
The concept of immobilizing indicator biomolecules onto conductive polymer substrates as well as the development of chemical and biological sensor devices that are based on electroconductive polymers in general is an area that has attracted considerable recent attention. See, for instance:
(1) A. Guiseppi-Elie, U.S. Pat. No. 5,766,934;
(2) M. Umana and J. Waller, Anal. Chem. 1986, 58, 2979-2983;
(3) N. C. Foulds and C. R. J. Lowe, Chem. Soc., Faraday Trans. 1 1986, 82, 1259-1264;
(4) C. Iwakura, Y. Kajiya and H. Yoneyama, J. Chem. Soc., Chem. Commun. 1988, 15, 1019;
(5) T. Matsue, et. al. J. Electroanal. Chem. Interfacial Electrochem. , 1991, 300, 111-117;
(6) M. Malmors, U.S. Pat. Nos. 4,334,880 and 4,444,892;
(7) M. K. Malmors, J. Gulbinski, III, and W. B. Gibbs, Jr. Biosensors, 1987/88, 3, 71.
However, all of these electroactive biosensors are designed to operate in aqueous environments, not in air. The present invention, as subsequently discussed, also allows for the detection of the chemical or/and biological agents in aqueous environments, but it has the further advantage of detecting these agents in gaseous environments, such as air, as well.
In general, these devices are formed from thin films of electroconductive polymer fabricated on a pattern of microsensor electrodes, which are, in turn, formed on an insulating substrate. Sensor devices that exploit the transducer-active responses of electroactive polymers may be conductometric, as discussed, for example, in:
(8) A. J. Lawrence and G. R. Moores, Europ. J. Biochem. 1972, 24, 538-546;
(9) D. C. Cullen, R. S. Sethi and C. R. Lowe, Anal. Chim. Acta 1990, 231, 33-40.
A number of ways to cause the transducer-active conductometric response has been described. The prior art teaches the use of the large change in electrical impedance for that purpose. See, for example:
(10) A. Guiseppi-Elie and A. M. Wilson, Proceedings 64th Colloid. and Surf Sci. Symp., Jun. 18-20, 1990, Leigh University, Lehigh, Pa.;
(11) T. Matsue, et. al., J. Chem. Soc., Chem. Commun. 1991, 1029-1031;
(12) M. Nishizawa, T. Matsue and I. Uchida, Anal. Chem. 1992, 64, 2642-2644;
(13) D. T. Hoa, et. al., Anal. Chem. 1992, 64, 2645-2646;
(14) Guiseppi-Elie, A. U.S. Pat. No. 5,312,762;
A conductometric response that accompanies oxidation and or reduction of the polymer, the amperometric response, has also been described. See, for example:
(15) L. Gorton, et. al., Anal. Chim. Acta 1991, 249, 43-54.
The use of redox mediation and/or electrocatalysis to cause the transducer-active conductometric response has been also described. See, for example:
(16) M. Gholamian, et. al., Langmuir, 1987, 3; 741;
(17) Y. Kajiya, et. al., Anal. Chem. 1991, 63, 49;
(18) Z. Sun and H. Tachikawa, Anal. Chem. 1992, 64, 1112-1117.
In particular, the potentiometric method, when the electrode potential change that accompanies changes in polymer redox composition is measured, was used. See, for example:
(19) S. Dong, Z. Sun, and Z. Lu, J. Chem. Soc., Chem. Commun. 1988, 993;
(20) S. Dong, Z. Sun , and Z. Lu, Analyst 1988, 113, 1525;
(21) Z. Lu, Z. Sun and S. Dong, Electroanalysis, 1989, 1, 271;
(22) A. E. Karagozler, et. al., Anal. Chim. Acta 1991, 248, 163-172;
(23) Y. L. Ma, et. al., Anal. Chim. Acta 1994 289 21-26.
As will be shown below, the detection of the chemical and/or biological agents in accordance with one aspect of the present invention measures transducer-active conductometric response as a result of a morphological change in a polymer film. None of the prior art mentioned above teaches or discloses the measurement of the response as a result of such change.
As subsequently discussed, another aspect of the present invention takes advantage of the encapsulation of indicator substances within sol-gel matrices. The encapsulation of indicator biomolecules within the pores of sol-gel matrices have been described and used for manufacturing of optical biosensors.
See, for example:
(24) Bakul C. Dave, et. al., Anal. Chem., 1994, 66, 1120A-1127A.
There are also several examples of conductive polymer composite films in sol-gel matrices. See,.for example:
(25) Y. Wei, et al., Chem. Mater., 1995, 7, 969.
Furthermore, conductive polymer based sensors have been developed for detecting volatile organic compounds in air, along with chemical weapon simulants. See, for example:
(26) F. G. Yamagishi, et al., Proc. of the SPE Annual-Technical Conference and Exhibits, ANTEC 98, XLIV, 1335 (1998).
Other sensor technologies include surface acoustic wave devices (which require complex frequency counting electronics), mass spectroscopy, infrared spectroscopy, and gas chromatography, or some combination or combinations of these methods. These techniques are currently being developed but are primarily directed toward laboratory analysis rather than field application. All of the existing methods of analysis and detection of biological pathogens and chemical agents have serious disadvantages of having large size, long analysis times, complicated electronics support, lack of specificity and high cost.
In view of the foregoing, there is a need for a simple, inexpensive and accurate sensor for detection of biological pathogens and chemical agents. A sensor is needed which is also low power, compact, rugged, highly selective, and adaptable to field application for detection of vapor phase pathogens in real time without the need for involving xe2x80x9cwetxe2x80x9d chemistry. There is no known prior art which teaches a sensor satisfying all these requirements.
The present invention provides such a sensor by combining conductive polymer transducers and encapsulated sol-gel techniques. The combination of these approaches is not found in any other sensor device for the detection of biological or chemical materials.
The present invention provides a sensor that can detect biological pathogens and chemical agents with unsurpassed sensitivities in the sub-part-per-million range, and possibly into the sub-part-per-billion regimes with good selectivity (low false alarm rate) in the vapor state in real time.
The sensor of the present invention avoids the problems with selectivity and has further advantages by operating passively in an ambient atmosphere without the need for concentrators to detect pathogens in air. Furthermore, the sensor of this invention can be equipped with communication capability so that a multitude of sensors could be deployed and their position and response to the environment, as communicated to a central control site, would provide a mapping of any potential hazard.
In accordance with one aspect of this invention, the sensor comprises a dielectric substrate, on which metal interdigitated (comb-like) electrodes are deposited. The substrate having such electrodes is then further coated with a thin film derived from the coupling of a conductive polymer and a sol-gel-derived material. The conductive polymer acts as the tranducer and the sol-gel material encapsulates, or is attached to, an indicator biomolecule (e.g., enzyme, antibody, antigen, etc.) specific to interacting with the target pathogen.
The conductive polymer comprises linear, highly conjugated polymers, which have an ability to conduct electricity by generating (by being oxidized or reduced) unpaired electrons traveling along the n-electron cloud of such a highly conjugated system. The conductivity is anisotropic in nature and is greatest in the direction along the chain, although there is some cross-talk between the adjacent polymeric chains, especially in macroscopic cases.
When the conductive polymer is prepared as a thin film, the direction of its polymeric chains is random, thus making an overall morphology of such thin polymeric films essentially amorphous.
The interaction-of the indicator biomolecule and the pathogen causes a morphological alteration in the material of the sensor because of a redistribution of the chains,with respect to each other, even on a microscopic scale, resulting in changes in distances between the chains and in the degree of cross-talk. Any influence causing a morphological change in the conductive polymer leads to a modulation of the conductivity of such a polymer. This modulation is detected by applying a voltage and registering the change in current.
The interaction of the indicator of chemical substances and the chemical substance may likewise cause a morphological alteration in the conductive polymer material of the sensor. Thus, chemical substances having toxic or pathogenic effects to certain biological moieties can be detected through this technique of the morphological alteration followed by the registering the conductivity modulation. For instance, some organophosphorus molecules (i.e., fungicides, insecticides, nerve-paralytical gases) selectively interact with acetylcholineesterase so that the latter can be immobilized and used as an indicator molecule for these organophosphorus compounds. Other indicator molecules can detect, in the same fashion, mixtures of even relatively inert aromatic hydrocarbons, such as benzene, toluene, ethylbenzene, and xylene.